Godowsky and Duane, in U.S. Pat. No. 2,870,012, disclose a solvent-shifting process for preparing microdispersions of color coupler compounds comprising at least one acid group (carboxyl or sulfonic acid).
Townsley and Trunley, in U.K. Pat. No. 1,193,349, disclose a solvent-shifting and pH-shifting process in the presence of a protective colloid for dispersing couplers as amorphous colloidal dispersions. Their process is applied to couplers that have no sulphonic acid or carboxylic acid solubilizing groups and that are soluble in a mixture of water-miscible organic solvent and aqueous alkali.
Webb et at. in U.S. Pat. No. 4,490,461, disclose a process for the preparation of a photographic material comprising at least one silver halide emulsion layer and which contains in at least one layer a photographically useful compound selected from the group consisting of developing agents, color couplers, optical brighteners, filter dyes, or acutance dyes. Said process comprises forming a solution of a photographically useful compound, a compound capable of being cross-linked, and a cross-linking agent for the cross-linkable compound, effecting cross-linking of the cross-linkable compound to form a cross-linked solid, isolating the solid and milling the solid to form particles of 0.1-0.5 .mu.m in size, dispersing the particles in a colloid binder coating solution, coating this solution on a photobase and drying the layer.
Bagchi, in U.S. Pat. Nos. 4,970,139 and 5,089,380, discloses methods of preparing precipitated coupler dispersion with increased photographic activity. Said methods comprise steps to simultaneously precipitate hydrophobic couplers in the form of small particles and wherein said particles incorporate at their instant of formation water-insoluble coupler solvents.
Chari et al., in U.S. Pat. No. 5,008,179, disclose the preparation of amorphous coupler dispersions by pH and solvent shifting and the mixing of said coupler dispersions with dispersions of permanent solvent immediately prior to preparing light sensitive coating melts. This process of combining permanent solvent with amorphous coupler dispersion minimizes certain difficulties arising from crystallization of said coupler during storage of the coupler dispersion. Chari et al. disclose the preparation of permanent solvent dispersions wherein the permanent solvent is loaded into a polymeric latex.
Langen et al., in U.K. Pat. No. 1,570,362 disclose the use of solid particle milling methods such as sand milling, bead milling, dyno milling, and related media, ball, and roller milling methods for the production of solid particle dispersions of photographic additives such as couplers, UV-absorbers, UV stabilizers, white toners, stabilizers, and sensitizing dyes.
Henzel and Zengerle, in U.S. Pat. No. 4,927,744, disclose photographic elements comprising solid particle dispersions of oxidized developer scavengers. Said dispersions are prepared by precipitation and by milling techniques such as ball-milling.
Boyer and Caridi, in U.S. Pat. No. 3,676,147, disclose a method of ball-milling sensitizing dyes in organic liquids as a means of spectrally sensitizing silver halide emulsions. Langen et al., in Canadian Patent No. 1,105,761, disclose the use of solid particle milling methods and processes for the introduction of sensitizing dyes and stabilizers in aqueous silver salt emulsions. Swank and Waack, in U.S. Pat. No. 4,006,025, disclose a process for dispersing sensitizing dyes, wherein said process comprises the steps of mixing the dye particles with water to form a slurry and then milling said slurry at an elevated temperature in the presence of a surfactant to form finely divided particles. Onishi et al., in U.S. Pat. No. 4,474,872, disclose a mechanical grinding method for dispersing certain sensitizing dyes in water without the aid of a dispersing agent or wetting agent. This method relies on pH control in the range of 6-9 and temperature control in the range of 60.degree.-80.degree. C.
Factor and Diehl, in U.S. Pat. No. 4,948,718, disclose solid particle dispersions of dyes for use as filter dyes in photographic elements. They disclose that such dyes can be dispersed as solid particle dispersions by precipitating or reprecipitating (solvent or pH shifting), by ball-milling, by sand-milling, or by colloid-milling in the presence of a dispersing agent.